Process for hydroformylating short-chain olefins using a heterogenized catalyst system without ionic liquid

ABSTRACT

The invention relates to a process for hydroformylating short-chain olefins, especially C2 to C5 olefins, in which the catalyst system is in heterogenized form on a support of a porous ceramic material, and to plants for performing this process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 119 patent application which claimsthe benefit of European Application No. 18198787.6 filed Oct. 5, 2018,which is incorporated herein by reference in its entirety.

FIELD

The project that led to this patent application was financed under GrantAgreement No. 680395 from the European Union Horizon 2020 Research andInnovation Programme.

The present invention relates to a process for hydroformylatingshort-chain olefins, especially C2 to C5 olefins, in which the catalystsystem is present in heterogenized form on a support of a porous ceramicmaterial, and to plants for performing this process.

BACKGROUND

Hydroformylation is one of the most important reactions in industrialscale chemistry, having an annual global production capacity of severalmillion tonnes. This involves reacting alkenes (olefins) with a mixtureof carbon monoxide and hydrogen (also: synthesis gas or syngas) using acatalyst to give aldehydes, which are important and valuableintermediates in the production of chemical bulk products such asalcohols, esters or plasticizers.

Hydroformylation is conducted exclusively under homogeneous catalysis onthe industrial scale. The soluble transition metal catalyst systems aretypically based on cobalt or rhodium, which is often used together withphosphorus-containing ligands, for example phosphines or phosphites, forthe hydroformylation of comparatively short-chain olefins.

There are various problems in the known processes, and these areespecially linked to the fact that both rhodium and cobalt and compoundsthereof are comparatively costly. There is a high level of energyexpenditure and complex chemical engineering in order to verysubstantially avoid losses of catalyst during the hydroformylationprocess, for example by catalyst recycling steps, some of them verycomplex. Moreover, product purification steps are becoming more complexin order to ensure that as far as possible no catalyst residues remainin the product.

Further problems with the known homogeneously catalysed processes arethe stability of the ligands, which have to withstand thehydroformylation conditions, such as temperature, pressure, pH etc., andconsumption of the solvent used during the process, which can becompensated for by replenishment.

In order to get round the aforementioned problems in the homogeneouslycatalysed hydroformylation, there has been development ofhydroformylation methods in which the catalyst is heterogenized,especially by immobilization on a support material (cf. introductorydiscussion in WO 2015/028284 A1). The terms “heterogenization” and“immobilization” should accordingly be understood such that the catalystis immobilized by formation of a thin liquid film with the aid of anionic liquid on the surface and/or in the pores of a solid supportmaterial and there is no reaction solution in the conventional sense inwhich the catalyst is homogeneously dissolved.

With regard to the immobilization/heterogenization, the alreadymentioned WO 2015/028284 A1 discloses what are called SILP systems(SILP=Supported Ionic Liquid Phase), in which the catalyst system isimmobilized with rhodium, iridium or cobalt as central atom, especiallyon a porous silicon dioxide support using an ionic liquid.

It is thought that the ionic liquid acts as a catalyst carrier/as asolvent, thus helping to immobilize the catalyst system on the support.However the problem with ionic liquids is that these are comparativelyexpensive and in some cases not toxicologically harmless.

The problem addressed by the present invention was that of providing asingle-stage or multistage hydroformylation process in which aheterogenized catalyst system that does not have the aforementionedproblems is used in a hydroformylation step.

SUMMARY

This problem is solved according to the present invention in that asingle-stage or multistage hydroformylation process comprises at leastone hydroformylation step in which a catalyst system in heterogenizedform on a support of a porous ceramic material is used without ionicliquid.

DETAILED DESCRIPTION

The present invention thus provides a process for hydroformylating C2 toC5 olefins, wherein the hydroformylation comprises one or morehydroformylation steps, characterized in that in at least onehydroformylation step a feed mixture comprising the C2 to C5 olefins issubjected to a hydroformylation with synthesis gas in the presence of acatalyst system comprising a metal from group 8 or 9 of the PeriodicTable of the Elements, at least one organic phosphorus-containing ligandand a stabilizer, in a reaction zone, wherein the feed mixture and thesynthesis gas are passed over a support composed of a porous ceramicmaterial on which the catalyst system is in heterogenized form,

the catalyst system comprises no ionic liquid; and

the support is a monolith, i.e. a block of a ceramic material, to whicha washcoat composed of the same or a different ceramic material withrespect to the ceramic material of the support is applied.

The feed mixture used may be any mixture comprising C2 to C5 olefins,especially ethene, propene, 1-butene, 2-butene, 1-pentene or 2-pentene,as reactants. The amount of olefins in the feed mixtures shouldnaturally be high enough to be able to economically conduct ahydroformylation. This especially includes technical mixtures from thepetrochemical industry, for example raffinate streams (raffinate I, IIor III) or crude butane. According to the present invention, crudebutane comprises 5% to 40% by weight of butenes, preferably 20% to 40%by weight of butenes (the butenes are composed of 1% to 20% by weight of1-butene and 80% to 99% by weight of 2-butene), and 60% to 95% by weightof butanes, preferably 60% to 80% by weight of butanes.

In the case of an at least two-stage hydroformylation feed mixtures mayalso be (gaseous) outputs from another hydroformylation. If the processaccording to the invention comprises at least two hydroformylation stepsthe step in which the catalyst system heterogenized on a support made ofa porous ceramic material is used without ionic liquid is at least thesecond hydroformylation step. The olefins unconverted in the firsthydroformylation step may then still be converted using the catalystsystem according to the invention. Between the hydroformylation stepsthere may be arranged a physical separation with which the gaseousoutput from the first hydroformylation is separated into at least onephase rich in unconverted olefins and at least one phase rich in productaldehyde. The phase rich in unconverted olefins is then subjected to thesecond hydroformylation.

The catalyst system used in the hydroformylation step according to theinvention preferably comprises a transition metal from group 8 or 9 ofthe Periodic Table of the Elements, especially iron, ruthenium, iridium,cobalt or rhodium, more preferably cobalt or rhodium, at least oneorganic phosphorus-containing ligand and a stabilizer.

The stabilizer is preferably an organic amine compound, more preferablyan organic amine compound containing at least one2,2,6,6-tetramethylpiperidine unit of formula (I):

In a particularly preferred embodiment of the present invention, thestabilizer is selected from the group consisting of the compounds of thefollowing formulae (I.1), (I.2), (I.3), (I.4), (I.5), (I.6), (I.7) and(I.8):

-   -   where n is an integer from 1 to 20;

-   -   where n is an integer from 1 to 12;

-   -   where n is an integer from 1 to 17;

-   -   where R is a C6- to C20-alkyl group.

For all film-forming components, i.e. in this case the stabilizer, thegas solubility for the reactants should be better than the gassolubility of the products. In that way alone, it is possible to achievepartial physical separation between reactant olefins used and productaldehydes formed. In principle, other film-forming substances would alsobe conceivable for the purpose, but it should be ensured that there isno elevated high boiler formation and/or that the resupply of thereactant olefins is restricted.

The organic phosphorus-containing ligand for the catalyst systempreferably has the general formula (VI)

R′−A−R″−A−R′″  (VI)

where R′, R″ and R′″ are each organic radicals, with the proviso that R′and R′″ are not identical, and each A is a bridging —O—P(—O)₂—group,where two of the three oxygen atoms —O—are respectively bonded to R′radical and R′″ radical. The organic R′, R″, R′″ radicals preferably donot contain a terminal trialkoxysilane group.

In a preferred embodiment, R′, R″ and R′″ in the compound of the formula(VI) are preferably selected from substituted or unsubstituted1,1′-biphenyl, 1,1′-binaphthyl and ortho-phenyl groups, especially fromsubstituted or unsubstituted 1,1′-biphenyl groups, with the proviso thatR′ and R′″ are not identical. More preferably, the substituted1,1′-biphenyl groups in the 3,3′ and/or 5,5′ positions of the1,1′-biphenyl base skeleton have an alkyl group and/or an alkoxy group,especially a C1-C4-alkyl group, more preferably a tert-butyl and/ormethyl group, and preferably a C1-C5-alkoxy group, more preferably amethoxy group.

According to the invention, the aforementioned catalyst system is inheterogenized form on a support of a porous ceramic material. In thecontext of the present invention, the expression “heterogenized on asupport” is understood to mean that the catalyst system is immobilizedvia formation of a thin, solid or liquid film with the aid of astabilizer on the inner and/or outer surface of a solid supportmaterial. The film may also be solid at room temperature and liquidunder reaction conditions.

The inner surface of the solid support material especially comprises theinner surface area of the pores and/or channels. The concept ofimmobilization includes both the case that the catalyst system and/orthe catalytically active species is in dissolved form in the solid orliquid film and the case that the stabilizer acts as an adhesionpromoter or the catalyst system is adsorbed on the surface, but is notin chemically or covalently bound form on the surface.

According to the invention, there is thus no reaction solution in theconventional sense in which the catalyst is homogeneously dissolved;instead, the catalyst system is dispersed on the surface and/or in thepores of the support.

The porous ceramic material is preferably selected from the groupconsisting of a silicate ceramic, an oxidic ceramic, a nitridic ceramic,a carbidic ceramic, a silicidic ceramic and mixtures thereof.

The silicate ceramic is preferably selected from aluminosilicate,magnesium silicate, and mixtures thereof, for example bentonite. Theoxidic ceramic is preferably selected from γ-alumina, α-alumina,titanium dioxide, beryllium oxide, zirconium oxide, aluminium titanate,barium titanate, zinc oxide, iron oxides (ferrites) and mixturesthereof. The nitridic ceramic is preferably selected from siliconnitride, boron nitride, aluminium nitride and mixtures thereof. Thecarbidic ceramic is preferably selected from silicon carbide, boroncarbide, tungsten carbide or mixtures thereof. Also conceivable aremixtures of carbidic and nitridic ceramic, called the carbonitrides. Thesilicidic ceramic is preferably molybdenum silicide. The supportaccording to the present invention to which the catalyst system isapplied preferably consists of a carbidic ceramic.

The support is a monolith, meaning that the support of the porousceramic material consists of a block (a three-dimensional object) of aceramic material. The block may either be in one-piece form or consistof multiple, i.e. at least two, individual parts that may be joinedtogether to form the block and/or may be joined to one another in afixed or partable manner. But the support is more particularly not agranular material that can be used as catalyst bed in fixed bedreactors.

The support of the porous ceramic material is preferably a componentthat extends in three dimensions and may in principle have any geometricshapes in its cross section, for example round, angular, square or thelike. The component that extends in three dimensions and can be used assupport, in a preferred embodiment, has a longitudinal direction(direction of the longest extent) in main through-flow direction(direction in which the feed mixture and the synthesis gas flow from thereactor inlet to the outlet).

The support thus formed from the porous ceramic material has at leastone continuous channel in main through-flow direction. However, thechannel(s) may also be configured such that they are not completelycontinuous but are concluded at the opposite end from the reactor inlet,or the channel is closed toward this end. The support may also have atleast two or more channels. The diameter of the channels may be in therange from 0.25 to 50 mm, preferably in the range from 1 to 30 mm,further preferably in the range from 1.5 to 20 mm and more preferably inthe range from 2 to 16 mm. If a plurality of channels are present, thediameters of the channels may be the same or different. The diameter ofthe channels should especially be chosen by comparison with thediameter(s) of the overall support in such a way that mechanicalstability is not impaired.

Furthermore, the support of the ceramic material is porous, i.e. haspores. The catalyst system according to the invention is especially alsoin the liquid or solid film in these pores. The pore diameter ispreferably in the range from 0.9 nm to 30 μm, preferably in the rangefrom 10 nm to 25 μm and more preferably in the range from 70 nm to 20μm. Pore diameter can be determined by means of nitrogen adsorption ormercury porosimetry to DIN 66133 (1993-06 version).

In a preferred embodiment, the support has at least partly continuouspores that extend from the surface to the channels and/or from onechannel to the next channel(s). It is also possible that multiple poresare connected to one another and hence overall form a single continuouspore.

The production of the support from a porous ceramic material on whichthe catalyst system is in heterogenized form is effected as describedbelow: What is called a washcoat is additionally applied to the supportcomposed of the ceramic material, and is composed of the same or adifferent ceramic material with respect to the ceramic material of thesupport, especially a ceramic material selected from the aforementionedceramic materials, preferably silicon oxide.

The washcoat itself may be porous or nonporous; preferably the washcoatis nonporous. The particle size of the washcoat is preferably 5 nm to 3μm, preferably 7 nm to 700 nm. The washcoat is used to introduce or togenerate the desired pore size and/or to increase the surface area ofthe support. The washcoat can especially be applied by means of dipping(dip-coating) into a washcoat solution containing the ceramic materialof the washcoat, possibly also as a precursor. The amount of thewashcoat on the support is ≤20% by weight, preferably ≤15% by weight,more preferably ≤10% by weight, based on the overall amount of thesupport.

The catalyst system is applied to the ceramic support thus produced withthe washcoat applied. For this purpose, a catalyst solution is firstproduced by mixing, especially at room temperature and ambient pressure,comprising at least one organic phosphorus-containing ligand, at leastone metal precursor, for example chlorides, oxides, carboxylates of therespective metal, at least one stabilizer and at least one solvent.According to the invention, the catalyst solution is explicitly made upwithout ionic liquid. The catalyst solution should especially beprepared in an inert environment, for example a glovebox. “Inertenvironment” in this case means a very substantially water- andoxygen-free atmosphere.

The solvent may be chosen from all solvent classes (protic, aprotic,polar or nonpolar). A prerequisite for the solvent is the solubility ofcatalyst system (ligand, metal precursor and stabilizer) and preferablyalso of the high boilers formed in the hydroformylation. Solubility canbe increased within the immobilization step by heating.

The solvent is preferably aprotic and polar, for example acetonitrileand ethyl acetate, or else aprotic and nonpolar, for example THF anddiethyl ether. It is also possible to use hydrochlorocarbons, forexample dichloromethane, as solvent.

The catalyst solution thus prepared is then contacted with the support(optionally including washcoat), for example by dipping (dip-coating) orby means of filling in a pressure vessel, for example directly in thereactor (in situ impregnation). If the catalyst solution is appliedoutside the reactor, the support must of course be installed into thereactor after the solvent has been removed. Preferably, the catalystsolution is applied directly to the support with the washcoat in thereactor because this can avoid possibly time-consuming installation anddeinstallation steps and possible contamination of the catalyst.

In the case of in situ impregnation, the reactor, prior to the filling,is purged with an inert gas, for example noble gases, alkanes ornitrogen. The purging can be conducted at 1 to 25 bar, preferably undera slightly positive pressure of 20 to 90 mbar, more preferably 30 to 60mbar, above standard pressure. The reactor can be cooled down prior tothe purging with inert gas in order to prevent the solvent in thecatalyst solution to be introduced from evaporating immediately.However, if the solvent has a boiling temperature greater than thereactor temperature, the cooling of the reactor can be dispensed with.

After the purging with inert gas, the pressure present can be released,for example via the pressure control system, preferably until thereactor is unpressurized, i.e. at ambient pressure (i.e. 1 bar).Otherwise, it is also possible to generate a vacuum in the reactor, forexample with a vacuum pump. In one configuration of the presentinvention, the reactor can again be purged with an inert gas asdescribed above after the pressure has been released or afterevacuation. This operation of releasing pressure/evacuating and purgingagain can be repeated as often as desired.

For the filling of the reactor, the catalyst solution is initiallycharged in a pressure vessel and preferably pressurized to a positiveinert gas pressure of 1 to 25 bar, more preferably a slightly positiveinert gas pressure of 20 to 90 mbar, preferably 30 to 60 mbar, abovereactor pressure.

The inert gas may be a noble gas, an alkane, for example butane, ornitrogen. The catalyst solution is then introduced into the reactor atsaid positive pressure to which the pressure vessel has beenpressurized, especially in a pressure-driven manner. The pressure in thepressure vessel on filling should be higher than in the reactor.Temperatures may be in the range from 20 to 150° C., and pressure from 1to 25 bar.

Another means of filling is that the reactor is kept under reducedpressure after purging with inert gas and the catalyst solution is drawninto the reactor by virtue of the reduced pressure. For the preparationof the catalyst solution, a solvent that boils under the prevailingvacuum or reduced pressure and the prevailing temperatures should beused.

The reactor can be filled with the catalyst solution via the normalinlets/outlets. Liquid distributors or nozzles within the reactor canensure homogeneous distribution of the catalyst liquid, as can pressuredrop internals or regulators for the metering rate that are optionallypresent. After the catalyst system has been applied, the solvent isremoved. This involves firstly discharging the remaining catalystsolution via the reactor outlet. Thereafter, solvent residues remainingin the reactor are evaporated by adjusting the pressure or increasingthe temperature.

In another embodiment, the adjustment of the pressure can also beconducted with a simultaneous increase in temperature. Depending on thesolvent, the temperature may be 20 to 150° C. Depending on the solvent,the pressure may be adjusted to a high vacuum (10⁻³ to 10⁻⁷ mbar), butaccording to the solvent and temperature, elevated pressures of a fewmbar up to several mbar are also conceivable.

The stabilizer remains in heterogenized form on the support with thecatalyst composed of the metal, especially cobalt or rhodium, and theorganic phosphorus-containing ligand.

The catalyst system can be applied to the support either directly in thereactor (in situ) or outside the reactor. In a preferred embodiment ofthe present invention, the catalyst system is applied directly in thereactor, i.e. in situ. After the solvent has been removed, the reactorcan be used immediately and charged with the feed mixture. This has theadvantage that no time-consuming installation and deinstallation stepsthat would result in a prolonged reactor shutdown are needed. Moreover,the size of the support in that case is no longer limited in thatsuitable spaces with inert environments are available in a particularsize. The size of the support can be chosen freely depending on thereactor design. A further problem is that the support must always betransported with exclusion of air, which is sometimes difficult toachieve.

On completion of application of the catalyst system to the support andof removal of the solvent, the plant, especially the reactor, can be runup, i.e. put into operation, by a two-stage or multistage startupprocedure.

The aim of the startup procedure is gentle activation of the catalystsystem and attenuation of the maximum starting activity of the catalystto prolong the service life of the catalyst system. Moreover, thestartup procedure is intended to prevent the formation of a liquid phasesince this can lead to deactivation, blocking and/or washout of thecatalyst system. This is because, particularly in the case of startup ofa freshly produced catalyst system (on the support) with concentratedreactant, it is possible to attain a reaction conversion maximum whichis also associated with maximum formation of by-products (high boilers).If the proportion of the high-boiling by-products, depending on theoperating conditions (pressure and temperature), exceeds a certainvalue, the result of this, owing to the vapour pressures of theindividual components that are dependent on the mixture present, can bethe formation of a liquid phase that can damage, block or wash out thecatalyst system.

According to the invention, the activation of the catalyst system ispreferably implemented with a rising conversion over a prolonged periodof time. Thus, for any combination of pressure, temperature andcomposition of the feed mixture, it is possible to calculate a maximumpermissible conversion for the formation of by-products that must not beexceeded in order not to allow the aforementioned problems to arise. Theconversion for the formation of by-products can also be ascertaineddepending on the conversion for the formation of the product aldehydes(=depending on the aldehyde concentration), meaning that the startupprocedure is guided by the maximum conversion of the feed olefins.

In the case of known long-term operating conditions of the reactor thatenable a reliable degree of conversion of the feed olefins of 20% to95%, preferably of 80%-95%, the startup procedure can be implemented insuch a way that the composition of the feed mixture which is run intothe reactor is altered stepwise without exceeding the maximum conversionof the feed olefins.

It is possible here to vary the composition of the feed mixture thatensures a reliable conversion of the olefins under long-term operatingconditions in such a way that, at a constant volume flow rate, theolefin content and/or the synthesis gas content is raised in at leasttwo stages, preferably more than three, especially four or more stages,without exceeding the maximum conversion of the feed olefins. For thispurpose, the technical feed mixture and synthesis gas mixture may besupplied in the first stage(s) with inert gases, for example N_(2,)argon, helium or the like.

Catalyst activity can decrease with increasing operating time, forexample as a result of the enrichment of high boilers and/or thecoverage or deactivation of active sites. The high boilers can lead toincreased condensation in the pores, such that the pores are accessibleto the reactant olefins more slowly, if at all. Secondly, someby-products can lead to breakdown of the catalyst system, which likewisedecreases the activity of the catalyst. A decrease in catalyst activitycan be ascertained, for example, from the drop in conversions orselectivities, especially via an appropriate analysis by means of Ramanspectroscopy, gas chromatography or mass flow meters (MFMs). Anotheroption would be model-based monitoring of the catalyst activity. Thiswould be a method independent of the operating conditions for monitoringthe catalyst activity, but also in order to extrapolate the progressionand hence support review/regeneration planning.

In the case of inadequate catalyst activity, the catalyst system inheterogenized form on the porous ceramic support can be exchanged. Forthis purpose, the catalyst or support can be purged once or more thanonce with a solvent in the reactor. The purging can demobilize andremove the catalyst system. The solvent may be one of the solventsmentioned for the preparation of the catalyst solution. The temperatureon solvent purging may be 20 to 150° C. The pressure on solvent purgingmay additionally be 1 to 25 bar.

After the purge, the support is reimpregnated once or more than once,especially by the above-described in situ impregnation of the support.The in situ impregnation is thus renewed and the heterogenized catalystsystem is freshly applied. The in situ reimpregnation can be conductedunder exactly the same conditions as described above for the first insitu impregnation.

Owing to the fact that the catalyst system is fully exchanged by purgingand reapplication, these steps can constantly be repeated as soon as thecatalyst activity drops again. A further advantage is that both highboilers and product aldehydes and breakdown products of the catalystsystem can be discharged. However, it should be ensured that theproperties of the support are not impaired by demobilization and in situreimpregnation. Otherwise, exchange of the porous ceramic support wouldhave to be conducted.

A further option is that the overall porous ceramic support on which thecatalyst system is in heterogenized form is exchanged. The catalystsystem in heterogenized form on the support (removed from the reactor)can then be exchanged as described above outside the reactor and storeduntil the next installation and use in the reactor. As mentioned above,an inert environment is required on application of the catalyst system,and therefore the handling and storage in the procedure mentioned ofdeinstallation and installation of the support should be effected undercorresponding conditions.

In principle, it is preferred to conduct a process in which there aremultiple reactors in parallel in the reaction zone and these are usedalternately. This involves using at least one reactor (a) for thehydroformylation according to the invention, i.e. one which is inoperation, and at least one reactor (b) which is in the wait state. Thisis understood to mean that, as soon as catalyst activity is found to nolonger be sufficient in reactor (a) which is in operation, the stream ofthe feed mixture is switched from this reactor (a) to the next reactor(b) in the wait state that is put into operation therewith. Reactor (a)is then transferred to regeneration mode, where the catalyst system isregenerated or demobilized as described and the support is newlyimpregnated, and then transferred into the wait position until it isswapped again with reactor (b). This principle can also be applied to 3or more reactors, where at least one reactor is in operation, one ormore reactors are simultaneously in the wait state and one or morereactors are simultaneously in regeneration mode.

The second hydroformylation step is preferably conducted under thefollowing conditions: The temperature in the second hydroformylationstep should be in the range from 65 to 200° C., preferably 75 to 175° C.and more preferably 85 to 150° C. The pressure should not exceed 35 bar,preferably 30 bar, more preferably 25 bar, during the secondhydroformylation step. The molar ratio between synthesis gas and thesecond feed mixture should be between 6:1 and 1:1. Optionally, the feedmixture can be diluted with inert gas, for example the alkanes presentin technical hydrocarbon streams.

A gaseous output comprising at least a portion of the product aldehydesformed and at least a portion of the unconverted olefins is preferablywithdrawn continuously from the reaction zone in which thehydroformylation according to the invention is conducted. The gaseousoutput may be subjected to one or more physical separation step(s) inwhich the gaseous output is separated into at least one phase rich inunconverted olefins and at least one phase rich in product aldehyde.

The physical separation can be conducted by known physical separationmethods such as condensation, distillation, centrifugation,nanofiltration or combinations of two or more of these, preferablycondensation or distillation.

In the case of a multistage physical separation, the phase rich inproduct aldehyde which is formed in the first physical separation issent to a second physical separation, especially a downstream removal ofaldehyde, in which the product aldehyde is separated from the othersubstances present in this phase, frequently alkanes and reactantolefins. The phase rich in unconverted olefin can be recycled to thehydroformylation step or, in the case of a multistage configuration, toone of the hydroformylation steps in order to hydroformylate the olefinspresent therein to the product aldehyde as well.

In the physical separation, as well as the phases mentioned, it is alsopossible to withdraw a purge gas stream having a composition identicalor at least similar to the phase rich in unconverted olefin. The purgegas stream can likewise be guided to the second physical separation oraldehyde removal in order to remove the product aldehyde present thereinand in order to discharge impurities (e.g. nitrogen in the synthesisgas) or inert substances (e.g. alkanes in the feed mixture) from thesystem. The impurities or inert substances can typically be removed inthe second physical separation as volatile substances, for example atthe top of a column.

The present invention also further provides a plant with which thepresent process can be conducted and which especially comprises areactor in which the hydroformylation step according to the invention isconducted. In addition, the plant may comprise a physical separationunit with which the gaseous output from the hydroformylation step isseparated into at least one phase rich in unconverted olefin and atleast one phase rich in product aldehyde, where this physical separationunit is arranged downstream of the hydroformylation step according tothe invention. Downstream of the first physical separation, there may bea second physical separation unit, especially an aldehyde removal unit,with which the product aldehyde is removed.

Even without further elaboration it is assumed that a person skilled inthe art will be able to utilize the description above to the greatestpossible extent. The preferred embodiments and examples are therefore tobe interpreted merely as a descriptive disclosure which is by no meanslimiting in any way whatsoever.

The present invention is more particularly elucidated hereinbelow withreference to examples. Alternative embodiments of the present inventionare obtainable analogously.

EXAMPLE:

Experiment 1: Preparation and Analysis of a Catalyst System notAccording to the Invention with Ionic Liquid

The support used was a monolith of silicon carbide having a length ofabout 20 cm and a diameter of about 25 mm. The support was porous andwas pretreated with a washcoat (SiO₂). The support had 31 channelshaving a diameter of about 3 mm. The support was inserted into a reactorand contacted with a catalyst solution containing Rh(acac)(CO)_(2,)Bisphephos (ligand), bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate(stabilizer), 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide ([EMIM][NTf_(2])/ ionic liquid) anddichloromethane as solvent, prepared by mixing in an inert environment(glovebox). For this purpose, after the reactor had been purged withnitrogen, the catalyst solution was introduced into the reactor with aslightly positive pressure. After the solvent had been removed from thereactor by discharge and evaporation, the catalyst system heterogenizedon the support was used for hydroformylation.

The feed mixture used was a hydrocarbon stream having the followingcomposition:

Amount (% by wt.) 1-butene/isobutene 19.14 cis-2-butene 19.10trans-2-butene 28.40 n-butane 30.80 isobutane 0.02 2-methylbutane 2.50

The feed mixture was guided into the reactor together with synthesis gas(molar synthesis gas:input mixture ratio=3.5:1) for hydroformylation ata gas volume flow rate of 390 ml/min. The hydroformylation was conductedat a temperature of 120° C. and a pressure of 10 bar. The totalconversion of butenes (i.e. the conversion of all butenes present in thefeed mixture) and the n/iso selectivity (ratio of linear to branchedproducts) was ascertained by gas chromatography via the productcomposition.

After an experiment duration of 500 hours, total conversion of buteneswas 27% and the n/iso selectivity 98%.

Experiment 2: Preparation and Analysis of a Catalyst System According tothe Invention without Ionic Liquid

The support used was a monolith of silicon carbide having a length ofabout 20 cm and a diameter of about 25 mm. The support was porous andwas pretreated with a washcoat (SiO₂).

The support had 31 channels having a diameter of about 3 mm. The supportwas inserted into a reactor and contacted with a catalyst solutioncontaining Rh(acac)(CO)_(2,) Biphephos (ligand),bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (stabilizer) anddichloromethane as solvent, prepared by mixing in an inert environment(glovebox). For this purpose, after the reactor had been purged withnitrogen, the catalyst solution was introduced into the reactor with aslightly positive pressure. After the solvent had been removed from thereactor by discharge and evaporation, the catalyst system heterogenizedon the support was used for hydroformylation.

The feed mixture used was a hydrocarbon stream with virtually identicalcomposition to that in Experiment 1. The feed mixture was guided intothe reactor together with synthesis gas (molar synthesis gas:feedmixture ratio=3.5:1) for hydroformylation at a gas volume flow rate of390 ml/min. The hydroformylation was conducted at a temperature of 120°C. and a pressure of 10 bar. The total conversion of butenes (i.e. theconversion of all butenes present in the feed mixture) and the n/isoselectivity (ratio of linear to branched products) was ascertained bygas chromatography via the product composition.

After an experiment duration of 500 hours, total conversion of buteneswas 56% and the n/iso selectivity 97%.

Experiment 3: Preparation and Analysis of an Silp Catalyst System NotAccording to the Invention

The catalyst system was prepared analogously to the preparation of thecatalytically active composition Rh(II) in WO 2015/028284 A1.

The feed mixture used was a hydrocarbon stream having the followingcomposition:

Amount (% by wt.) 1-butene/isobutene 27.40 cis-2-butene 15.00trans-2-butene 25.00 n-butane 29.50 isobutane 0.02 2-methylbutane 3.00

The feed mixture was guided into the reactor together with synthesis gas(molar synthesis gas:feed mixture ratio=3.5:1) for hydroformylation at agas volume flow rate of 390 ml/min. The hydroformylation was conductedat a temperature of 120° C. and a pressure of 10 bar. The totalconversion of butenes (i.e. the conversion of all butenes present in thefeed mixture) and the n/iso selectivity (ratio of linear to branchedproducts) was ascertained by gas chromatography via the productcomposition.

After an experiment duration of 500 hours, total conversion of buteneswas 25% and the n/iso selectivity 92%.

It is thus apparent from the series of experiments that theheterogenized catalyst systems according to the invention without ionicliquid have the advantage over the known SILP systems or systems withionic liquid that higher conversions and/or a higher linearity of theproducts (n/iso selectivity) can be achieved therewith.

1. Process for hydroformylating C2 to C5 olefins, wherein thehydroformylation comprises one or more hydroformylation steps, whereinin at least one hydroformylation step a feed mixture comprising the C2to C5 olefins is subjected to a hydroformylation with synthesis gas inthe presence of a catalyst system comprising a metal from group 8 or 9of the Periodic Table of the Elements, at least one organicphosphorus-containing ligand and a stabilizer, in a reaction zone,wherein the feed mixture and the synthesis gas are passed over a supportcomposed of a porous ceramic material on which the catalyst system is inheterogenized form, the catalyst system does not comprise any ionicliquid; and the support is a block of a ceramic material, to which awashcoat composed of the same or a different ceramic material withrespect to the ceramic material of the support is applied.
 2. Theprocess according to claim 1, wherein a gaseous output comprising atleast a portion of the product aldehydes formed and at least a portionof the unconverted olefins is withdrawn continuously from the reactionzone and the gaseous output is subjected to a physical separation stepin which the gaseous output is separated into at least one phase rich inunconverted olefins and at least one phase rich in product aldehyde. 3.The process according to claim 1, wherein the organicphosphorus-containing ligand in the hydroformylation catalyst system hasthe general formula (VI)R′−A−R″−A−R′″  (VI) where R′, R″ and R′″ are each organic radicals, withthe proviso that R′ and R′″ are not identical, and each A is a bridgingO—P(—O)2— group, where two of the three oxygen atoms —O— arerespectively bonded to R′ radical and R′″ radical.
 4. The processaccording to claim 1, wherein the stabilizer is an organic aminecompound containing at least one 2,2,6,6-tetramethylpiperidine unit offormula (I):


5. The process according to claim 1, wherein the porous ceramic materialof which the support consists is selected from the group consisting of asilicate ceramic, an oxidic ceramic, a nitridic ceramic, a carbidicceramic, a silicidic ceramic and mixtures thereof.
 6. The processaccording to claim 5, wherein the silicate ceramic is selected fromaluminosilicate, magnesium silicate, and mixtures thereof, for examplebentonite; the oxidic ceramic is selected from γ-alumina, α-alumina,titanium dioxide, beryllium oxide, zirconium oxide, aluminium titanate,barium titanate, zinc oxide, iron oxides (ferrites) and mixturesthereof; the nitridic ceramic is selected from silicon nitride, boronnitride, aluminium nitride and mixtures thereof; the carbidic ceramic isselected from silicon carbide, boron carbide, tungsten carbide ormixtures thereof; and the silicidic ceramic is molybdenum silicide. 7.The process according to claim 5, wherein the porous ceramic material ofwhich the support consists is a carbidic ceramic.
 8. The processaccording to claim 6, wherein the carbidic ceramic is selected fromsilicon carbide, boron carbide, tungsten carbide or mixtures thereof. 9.The process according to claim 1, wherein the amount of the washcoat onthe support is ≤20% by weight, based on the total amount of the support.10. The process according to claim 1, wherein the support composed ofthe ceramic material has one or more channels in main through-flowdirection.
 11. The process according to claim 1, wherein thehydroformylation step is conducted at a temperature in the range from 65to 200° C.
 12. The process according to claim 1, wherein the pressure inthe hydroformylation step is not greater than 35 bar.
 13. The processaccording to claim 2, wherein the organic phosphorus-containing ligandin the hydroformylation catalyst system has the general formula (VI)R′−A−R″−A−R′″  (VI) where R′, R″ and R′″ are each organic radicals, withthe proviso that R′ and R′″ are not identical, and each A is a bridgingO—P(—O)2—group, where two of the three oxygen atoms —O— are respectivelybonded to R′ radical and R′″ radical.
 14. The process according to claim2, wherein the stabilizer is an organic amine compound containing atleast one 2,2,6,6-tetramethylpiperidine unit of formula (I):


15. The process according to claim 2, wherein the porous ceramicmaterial of which the support consists is selected from the groupconsisting of a silicate ceramic, an oxidic ceramic, a nitridic ceramic,a carbidic ceramic, a silicidic ceramic and mixtures thereof.
 16. Theprocess according to claim 15, wherein the silicate ceramic is selectedfrom aluminosilicate, magnesium silicate, and mixtures thereof, forexample bentonite; the oxidic ceramic is selected from γ-alumina,α-alumina, titanium dioxide, beryllium oxide, zirconium oxide, aluminiumtitanate, barium titanate, zinc oxide, iron oxides (ferrites) andmixtures thereof; the nitridic ceramic is selected from silicon nitride,boron nitride, aluminium nitride and mixtures thereof; the carbidicceramic is selected from silicon carbide, boron carbide, tungstencarbide or mixtures thereof; and the silicidic ceramic is molybdenumsilicide.
 17. The process according to claim 15, wherein the porousceramic material of which the support consists is a carbidic ceramic.18. The process according to claim 16, wherein the carbidic ceramic isselected from silicon carbide, boron carbide, tungsten carbide ormixtures thereof.
 19. The process according to claim 2, wherein theamount of the washcoat on the support is ≤20% by weight, based on thetotal amount of the support.
 20. The process according to claim 2,wherein the support composed of the ceramic material has one or morechannels in main through-flow direction.